Refractory comet dust analogues by laser bombardment and arc discharge production: a reference frame for “dusty experiments” on-board ROSETTA

Abstract

A number of instruments included in the ROSETTA payload are aimed at characterising the cometary dust properties. An important issue will be the nature of these dusts that will include organic (CHON), mixed CHON-silicate, and silicate dust, and ice grains, that are probably arranged in more or less heterogeneous fluffy agglomerates. The dust can be completely amorphous, partially structured and crystalline and these grains may coexist at small scales. Laboratory analysis of the morphological, crystallographic and chemical properties of cometary grain analogues produced in controlled laboratory conditions will play a critical role in the success of the ROSETTA mission. The results obtained by these laboratory analysis can be used to test and calibrate the instruments that will be sent to comet 46P/Wirtanen by this mission. The interpretations of returned scientific data will strongly benefit by the comparison with data recorded by the instruments in ground tests for different classes of analogues previously well characterised with various analytical techniques in the laboratory. In this paper we describe our facilities to produce and characterise elemental carbon, hydrogenated carbon, silicate and mixed carbon-silicate grains by laser bombardment and arc discharge techniques. We use field emission scanning electron microscopy and transmission and analytical electron microscopy to identify the textures, morphologies and grain compositions and structures in analogue samples. Spectroscopy (from far ultraviolet to far infrared) is used to study their optical responses. Some analogue properties, e.g. grain texture and morphology, are similar to those detected in chondritic interplanetary dust particles that may include solid debris from periodic comets.